A vane oil pump has been disclosed in Patent document 1. This type of vane oil pump is often mounted on a vehicular automatic transmission and used for supplying hydraulic pressure for the purpose of controlling the automatic transmission.
Referring to FIG. 5, there is shown an explanatory drawing illustrating a vane oil pump 90 of a conventional example (a comparative example). FIG. 5a is a sectional view of the oil pump 90, whereas FIG. 5h is an enlarged view in and around an interconnection portion (a flow constriction 98) for interconnecting a pressure chamber 97 and a discharge passage 99.
Vane oil pump 90 shown in FIG. 5 is provided with an inner rotor 94 configured to rotate integral with a shaft 20, and an outer rotor 95 configured to surround the outer periphery of the inner rotor 94. These rotors, that is, inner rotor 94 and outer rotor 95 are housed in a pump chamber 920 formed in a body case 91 constructed by a housing 92 and a cover 93.
In this oil pump 90, spaces, which are defined between an external toothed portion formed on the outer periphery of inner rotor 94 and an internal toothed portion formed on the inner periphery of outer rotor 95, are displaced around the rotation axis X of the inner rotor, while periodically increasing and decreasing their volumes during rotation of inner rotor 94. That is, oil pump 90 utilizes the circumferential displacement of each individual space whose volume periodically increases and decreases, for pressurizing oil sucked from a suction port of the oil pump 90 and for discharging the pressurized oil through a discharge opening 960 formed in a wall member 96.
Also, in the oil pump 90, regarding the spaces, which are defined between the external toothed portion of the inner rotor 94 and the internal toothed portion of the outer rotor 95 both rotating, a plurality of spaces exist in the circumferential direction around the rotation axis X. When each of the spaces passes through the specified position corresponding to the discharge opening 960, its volume becomes narrowest, thereby permitting the oil in the space to be discharged through the discharge opening 960.
By the way, each of the plurality of spaces, which exist in the circumferential direction around the rotation axis X, intermittently passes through the discharge opening 960, and thus fluid-flow pulsation occurs in the oil discharged through the discharge opening 960.
Therefore, assuming that the discharge opening 960 has been connected directly to a downstream-side discharge passage 99, the aforementioned pulsation would be just transmitted to the oil flowing through a downstream-side oil passage 100.
In the oil pump 90 of the conventional example, the ring-shaped pressure chamber 97 is provided adjacent to the discharge opening 960 for reducing or dampening the fluid-flow pulsation of the oil discharged through the discharge opening 960 within the pressure chamber 97 and for supplying the oil whose pulsation has been reduced within the pressure chamber through the flow constriction 98 (serving as a flow control valve) via the downstream-side discharge passage 99 into the downstream-side oil passage 100.
On one hand, the flow constriction 98 exhibits an oil pulsation suppression function that the pulsation of oil supplied to the downstream-side discharge passage 99 is further suppressed. On the other hand, the flow constriction 98 serves as a flow resistance that impedes the flow of oil moving or flowing from the pressure chamber 97 toward the downstream-side discharge passage 99. Therefore, in the case that the oil pump 90 is driven by output rotation of a driving power source (for example, an engine), the fuel economy of a driving-power-source equipped vehicle may be deteriorated.
For the reasons discussed above, the abolition of the flow control valve (the flow constriction) has been studied or examined. However, suppose that the flow control valve has been abolished and thus the flow constriction 98 has been eliminated. In such a case, a contributory portion of the flow constriction 98 that contributes to a reduction of pulsation also disappears, and thus the pulsation of oil supplied to the downstream-side discharge passage 99 is undesirably increased.
Therefore, it would be desirable to suppress or prevent the pulsation in a downstream-side oil passage from being undesirably increased even when a flow control valve (a flow constriction), provided downstream of a discharge opening of an oil pump, has been abolished.